Advertise virtually anything here, with CPM banner ads, CPM email ads and CPC contextual links. You can target relevant areas of the site and show ads based on geographical location of the user if you wish.

OP, can you tell me, have you had any good experience finding clients for web design this way? Or you just think you will find them with cheap traffic bought?

I'd suggest you to invest in PPC if you want to promote your services. This is the one high quality traffic. Run ads on Google Adwords and that's it. No one here will sell you hq traffic for web design services, except the same PPC traffic for bigger price than you can buy, bidding yourself.

I think this might help you.
There are tons of resources and references you can find here: seoblogbuzz.com
From blogging, free tools, affiliate marketing, payment merchant, content network etc.
I got some free eBooks from the site.